Tay-Sachs and Sandhoff disease are inherited lysosomal storage disorders resulting from beta-hexosaminidase deficiency. Affected patients present with neurodegeneration, mental and motor deterioration, muscular flaccidity, blindness, dysarthria, impaired thermal sensitivity, increasing dementia and cherry-red spots in the macula of the eye. Depending on the clinical severity patients may reach a vegetative state followed by death as early as 2-4 years of life. The neurons of the brain, cerebellum, brain stem, spinal cord, trigeminal and spinal root ganglia display swollen vacuolated perikarya stored with excessive amounts of GM2 ganglioside, leading to aberrant neuronal function, microglia activation and brain inflammation. Based on these observations, we hypothesize that microglia activation and neuro-inflammation secondary to GM2 neuronal gangliosidosis contributes to neurodegeneration and disease development. To test this hypothesis, we propose to investigate neuronal storage and its effects on the microglia/monocyte/macrophage system in a mouse model of GM2 gangliosidosis (hexB-/-knockout). First, we will determine the role of GM2 gangliosidosis in brain inflammation by selectively rescuing neurons from beta-hexosaminidase deficiency. Second, we will investigate the role of peripheral blood mononuclear cells in GM2 gangliosidosis by inhibiting monocyte/macrophage infiltration into the brain. Subsequently, we will transduce bone marrow derived-cells with the therapeutic gene betaHex, capable of expressing both subunits of the human beta-hexosaminidase, and evaluate their efficacy in attenuating disease development in a fashion similar to that described after bone marrow transplantation. In the last specific aim, we will determine whether beta-hexosaminidase gene therapy administered intraperitoneally to hexB-/- P2 neonates can effectively transduce neurons, glia and peripheral blood mononuclear cells with the therapeutic gene betaHex. With this more of therapy we anticipate a resolution of GM2 storage and neuro-inflammation ultimately leading to amelioration of the clinical phenotype of the disease.